I just put a set of stock 6.0 317 heads on my ls1. when I went to put the plugs on (ngk tr6 pt number 4177) they threaded in fine, but they threaded in the heads so far by hand that I can't get a socket on the plug. it's almost like the holes for the plugs to go into before the threads are not big enough, or they aren't stopping like they are supposed to. Any ideas?

 

figured it out, spark plug socket was interfering with the turbo header. ugh have to pull the header back off now...

 

sounds like fun